The present invention is directed to golf balls and golf ball core compositions having good durability, high resilience, and including at least one high Vicat softening temperature thermoplastic material. The golf balls of the invention can have various layer constructions, e.g., multilayer cores, multilayer covers, multiple intermediate layers, etc. The invention also includes methods of forming such golf balls and portions thereof.
Golf ball manufacturers are constantly attempting to construct golf balls having a desirable combination of good xe2x80x9cfeel,xe2x80x9d distance, and durability. One way in which the properties of a golf ball may be adjusted is through the cover composition and construction of the ball. Conventional golf balls can be divided into several general types or groups: (1) one piece balls; (2) two piece balls; (3) wound balls; and (4) other balls with three or more layers. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Wound balls typically have either a solid rubber or fluid filled center around which many yards of a stretched elastic thread or yarn are wound. The wound core is then covered with a durable cover material, such as SURLYN(copyright), or a softer material, such as balata or a castable polyurethane. Wound balls are generally softer and provide more spin than the aforementioned two piece balls. Particularly with approach shots into the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.
Balls having a solid two piece construction are generally most popular with the average recreational golfer because they provide maximum distance and durability. Two piece balls commonly include a single solid core, usually formed of a crosslinked rubber. Solid cores are often made of polybutadiene that is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents and is covered by a tough, cut-resistant blended cover, such as SURLYN(copyright), an ionomer resin produced by E. I. Du Pont de Nemours and Co. of Wilmington, Del. The combination of the core and cover materials imparts a relatively high initial velocity to the ball resulting in improved distance. Due to the rigidity of these materials, two piece balls have a hard xe2x80x9cfeelxe2x80x9d when struck with a club and a lower spin rate, making these balls more difficult to draw or fade.
A number of golf ball manufacturers have introduced golf balls having three or more layers in an effort to overcome the undesirable aspects of conventional two-piece balls, such as their hard feel, while retaining their positive attributes, such as increased initial velocity and distance. These balls have multiple core layers, i.e., they include a center with one or more intermediate layers, and one or more cover layers.
Although a variety of factors affect which of these types of balls a player will use, all players desire a ball that is affordable and durable. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to develop low-cost, efficient manufacturing techniques that produce golf balls which are resistant to cutting and cracking, yet which exhibit desirable distance, spin rate, and compression.
The durability of a ball depends not only upon its cover, but upon its core as well. A number of elastomers such as polybutadiene, natural rubber, styrene butadiene rubber, and isoprene rubber are commonly used in fabricating golf ball cores. Polybutadiene is most commonly used to obtain desired golf ball properties. Manufacturers have added cross-linking agents, such as metallic salts of an xcex1,xcex2-unsaturated carboxylic acid, to the elastomeric core composition to achieve a desired resiliency, compression, and durability.
Some manufacturers have instead attempted to provided improved golf balls by surrounding polybutadiene solid centers with thermoplastic intermediate layers. For example, U.S. Pat. No. 4,337,946 discloses a golf ball having an intermediate layer of thermoplastic resin between a polybutadiene thread-wound center portion and an outer polyester elastomer cover layer which contributes to the ball""s impact and cutting resistance characteristics.
U.S. Pat. No. 4,919,434 discloses a golf ball having a solid core of more than 40% cis-1,4-polybutadiene and a cover having an inner layer of 0.1 to 2 mm thickness and an outer layer of 0.1 to 1.5 mm thickness. The inner layer is a thermoplastic resin, such as an ionomer, polyester elastomer, polyamide elastomer, thermoplastic urethane elastomer, propylene-butadiene copolymer, 1,2-polybutadiene, polybutene-1, and styrene-butadiene block copolymer, either individually or in combination.
U.S. Pat. No. 5,439,227 discloses a three-part golf ball having a rubber inner core, and an outer core formed by injection molding a mixture of 100 to 50 weight percent of a polyether ester type thermoplastic elastomer and 0 to 50 weight percent of an ethylene-(meth)acrylate copolymer ionomer.
While materials incorporating a thermoplastic into a polymer blend are known, the use of such blends in portions of a golf ball core is not known. For example, U.S. Pat. No. 4,972,020 discloses an inner cover layer having a modified block copolymer of a thermoplastic polymer and a modified block copolymer consisting essentially of a base block copolymer of a monovinyl substituted aromatic hydrocarbon polymer block and an olefinic compound polymer block having an ethylenic unsaturation degree not exceeding 20 percent, wherein the base block has a molecular unit having a carboxylic acid group and/or a group derived therefrom grafted thereto.
U.S. Pat. No. 5,093,423 discloses a method of making a thermoplastic elastomer produced by dynamic vulcanization of styrene-butadiene-styrene (xe2x80x9cSBRxe2x80x9d) rubber as a dispersed phase of crosslinked SBR, and a co-continuous matrix of styrene-ethylene-butylene-styrene (xe2x80x9cSEBSxe2x80x9d) and polypropylene.
U.S. Pat. No. 5,100,947 discloses a dynamically vulcanized composition of a polyolefin thermoplastic resin and an elastomer of a rubber material in which a major portion of fillers or specified additives are present in the resin.
U.S. Pat. No. 5,270,386 discloses a cover blend of vinyl aromatic copolymer and a poly(phenylene ether) concentrate containing poly(phenylene ether), a vinyl aromatic copolymer, polyamide, polycarbonate, polyester, poly(alkyl acrylate), and/or poly(alkyl methacrylate). The blend may optionally contain impact modifiers, thermoplastic molding materials including polyester, polystyrene, polyolefin, polyamide, polyvinyl chloride, polyurethane, polyacetal, and conventional additives, such as dyes and pigments.
While some of the references discussed herein describe the use of thermoplastics in forming a golf ball cover, a golf ball core or portion of a core that contains a blend of both thermoplastic and elastomeric materials is not disclosed. There has thus been a long-felt need, which is now satisfied by the present invention, for a golf ball core, or portion thereof, having a blend of at least one high Vicat softening thermoplastic and at least one elastomer to provide an increased geometric stability without substantially affecting the desired golf ball properties.
The present invention is directed to golf ball core compositions, and methods for forming golf ball cores of the compositions, having at least one elastomer and at least one thermoplastic or thermoplastic elastomer dispersed therein. The thermoplastic or thermoplastic elastomer preferably has a high Vicat softening temperature and high resilience. At least a portion of the compositions are crosslinked. In one embodiment, the at least one thermoplastic or thermoplastic elastomer has a hardness of at least about 15 Shore A, a dynamic shear storage modulus of at least about 104 dynes/cm2, a loss tangent no greater than 1 at 23xc2x0 C. and a frequency of 1 Hz, and a Vicat-softening temperature of at least about 38xc2x0 C. The golf balls of the invention typically have an Atti compression no greater than about 110 and a coefficient of restitution of at least about 0.7 when fired at an inbound speed of 125 ft/sec with a cover having a thickness of at least about 0.03 inches, a cover hardness of at least about 40 Shore D, and at least about 60 percent dimple coverage. The cores formed from the composition typically have a Bashore rebound of at least about 30 percent and at least one inner layer having a compression no greater than about 110. The composition preferably includes a vulcanized material composition having at least one natural or synthetic rubber, a metal salt of unsaturated acid, an initiator, and at least one thermoplastic or thermoplastic elastomer; and optionally, a density-modifying filler. In a preferred embodiment, the golf ball includes at least one intermediate layer situated between the cover and the core, wherein the intermediate layer has a hardness of at least about 15 Shore A and a specific gravity of at least about 0.7, and is formed from a vulcanized material composition comprising at least one rubber, a metal salt of xcex1,xcex2-unsaturated acid, an initiator, and at least one thermoplastic or thermoplastic elastomer having a hardness of at least about 15 Shore A, a dynamic storage modulus of at least about 104 dynes/cm2, a loss tangent no greater than 1 at 23xc2x0 C. and a frequency of 1 Hz, and a Vicat-softening temperature of at least about 38xc2x0 C.
The invention also encompasses golf balls including cores formed of the compositions disclosed herein. The cores can either be solid, fluid filled, or hollow, or they can contain two or more layers, i.e., any golf ball core construction may be used.
In one embodiment, the thermoplastic or thermoplastic elastomer has a Vicat-softening temperature of at least about 38xc2x0 C. In a preferred embodiment, the thermoplastic or thermoplastic elastomer has a Vicat-softening temperature of at least about 50xc2x0 C. In another embodiment, the thermoplastic or thermoplastic elastomer is substantially uniformly dispersed throughout the vulcanized material composition of the portion of the golf ball core.
In a further embodiment, the rubber component of the core is selected from the group of polybutadiene, polyisoprene, ethylene-propylene, styrene-butadiene, ethylene-propylene-diene rubber (EPDM), styrene-ethylene-butylene-styrene, and mixtures thereof, including functionalized derivatives thereof.
In another embodiment, the high Vicat-softening thermoplastic or thermoplastic elastomer of the golf ball core is a block polymer selected from the group of copoly(ether-ester), copoly(ether-amide), copoly(ester-amide), copoly(urethane-ether), copoly(urethane-ester), maleic anhydride grafted styrene-ethylene-butylene-styrene copolymers, and mixtures thereof.
In a further embodiment of the invention, the amount of thermoplastic or thermoplastic elastomer in the golf ball core is between about 1 to 50 parts per hundred of the total parts of the rubber, and more preferably between about 5 to 30 parts per hundred of the total parts of the rubber.
In another embodiment, the thermoplastic or thermoplastic elastomer has a Vicat softening temperature of from about 38xc2x0 C. to 190xc2x0 C. In a preferred embodiment, the Vicat softening temperature is from about 50xc2x0 C. to 180xc2x0 C., and in a more preferred embodiment from about 60xc2x0 C. to 150xc2x0 C.
In one embodiment of this invention, the thermoplastic or thermoplastic elastomer of the golf ball core has a Shore D hardness from about 20 to 75, more preferably 20 from about 25to 60.
In a preferred embodiment, the golf ball has a coefficient of restitution of greater than about 0.7. In a more preferred embodiment, the golf ball has a coefficient of restitution of greater than about 0.75. In a most preferred embodiment, the golf ball has a coefficient of restitution of greater than about 0.775.
In another embodiment, the thermoplastic or thermoplastic elastomer of the golf ball core has a flexural modulus from about 500 psi to 150,000 psi.
The golf ball core of this invention may further include, but is not limited to, an ingredient independently selected from the group of density-modifying fillers, foaming agents, metals, lubricants, colorants, antioxidants, and mixtures thereof. Several of these embodiments and preferred embodiments are also applicable to the method described below.
The present invention further encompasses a method of forming a portion of a golf ball core wherein a first mixture including at least one rubber and at least one thermoplastic or thermoplastic elastomer is mixed at a first temperature. The first mixture is then cooled to a second temperature which is below an activation temperature of a free-radical initiator capable of facilitating crosslinking of the first mixture. A second mixture is then created by combining the free-radical initiator and the first mixture and, if desired, further combining a crosslinking agent or other ingredients. The second mixture is then heated to a third temperature equal to or greater than the activation temperature of the free-radical initiator to cure the second mixture so as to form the portion of the golf ball core. The second temperature is typically above the first temperature and below the activation temperature of the free-radical initiator.
The method of the invention may further include selecting the crosslinking agent from the group of alpha- or beta- unsaturated carboxylic acids. In a preferred embodiment, the metal salts are selected from diacrylates, dimethacrylates, monomethacrylates, monoacrylates, and mixtures thereof.
The method may further include adding a free-radical initiator to the second mixture. This free-radical initiator is preferably selected from the group of dicumyl peroxide, 1,1-di(t-butylperoxy)-3,3,5-trimethyl cyclohexane, bis(t-butylperoxy)-diisopropylbenzene, 2,5-dimethyl-2,5 di(t-butylperoxy) hexane, di-t-amyl peroxide, di-t-butyl peroxide, and mixtures thereof.
In one embodiment, the first temperature is selected to be in the range from about 38xc2x0 C. to 190xc2x0 C., more preferably from about 50xc2x0 C. to 180xc2x0 C.
In another embodiment, the second temperature is selected to be in the range from about 16xc2x0 C. to 80xc2x0 C., more preferably from about 10xc2x0 C. to 55xc2x0 C.
The method of this invention may further comprise adding to the first mixture and/or the second mixture an ingredient independently selected from the group of density-modifying fillers, foaming agents, metals, lubricants, colorants, antioxidants, and mixtures thereof.
The method further includes forming a cover concentrically about the portion of the golf ball core so as to form a golf ball.
The present invention is also directed to a golf ball including a core, wherein the core comprises at least one layer formed of a composition including at least one rubber, a metal salt of an xcex1,xcex2-unsaturated acid, an initiator, and at least one thermoplastic material having a Vicat-softening temperature of at least about 38xc2x0 C., an inner cover disposed about the core, and an outer cover disposed about the inner cover.
In one embodiment, the at least one thermoplastic material preferably has at least one of a hardness of at least about 15 Shore A, a dynamic storage modulus of at least about 104 dynes/cm2, or a loss tangent no greater than 1 at 23xc2x0 C. and a frequency of 1 Hz.
The at least one thermoplastic material is preferably a thermoplastic elastomer. In one embodiment, the thermoplastic elastomer is a block polymer selected from the group consisting of a copoly(ether-ester), copoly(ether-amide), copoly(ester-amide), copoly(urethane-ether), copoly(urethane-ester), maleic anhydride grafted styrene-ethylene-butylene-styrene copolymers, and mixtures thereof.
The amount of said at least one thermoplastic material is preferably from about 1 to 50 parts per hundred of the total parts of the rubber. The at least one rubber is preferably selected from the group consisting of polybutadiene, polyisoprene, ethylene-propylene, styrene-butadiene, ethylene-propylene-diene rubber, a polymer of ethylene-propylene diene monomer, styrene-ethylene-butylene-styrene copolymer, and mixtures thereof, including functionalized derivatives thereof.
In one embodiment, the core has a diameter of about 1.55 inches or less.
In another embodiment, the outer cover comprises a castable reactive liquid material, preferably cast polyurethane. The outer cover preferably has a hardness from about 30 Shore D to about 60 Shore D and a thickness from about 0.02 inches to about 0.045 inches.
In yet another embodiment, the inner cover includes at least one material selected from the group consisting of ionomers, thermoplastic or thermoset polyurethanes, polyetheresters, polyetheramides, or polyesters, dynamically vulcanized elastomers, functionalized styrene-butadiene elastomers, metallocene polymers, polyamides such as nylons, acrylonitrile butadiene-styrene copolymers (ABS), and blends thereof. The inner cover preferably has a thickness from about 0.01 inches to about 0.05 inches and a hardness of about 65 Shore D or greater.
The present invention is also directed to a golf ball including a core including at least two layers, wherein at least one of the core layers is formed of a composition including at least one rubber, a metal salt of an xcex1,xcex2-unsaturated acid, an initiator, and at least one thermoplastic material, preferably a thermoplastic elastomer, having a Vicat-softening temperature of at least about 38xc2x0 C., an inner cover disposed about the core, and an outer cover disposed about the inner cover.
The thermoplastic elastomer is preferably a block polymer selected from the group consisting of a copoly(ether-ester), copoly(ether-amide), copoly(ester-amide), copoly(urethane-ether), copoly(urethane-ester), maleic anhydride grafted styrene-ethylene-butylene-styrene copolymers, and mixtures thereof.
In one embodiment, the at least one thermoplastic material has at least one of a hardness of at least about 15 Shore A, a dynamic storage modulus of at least about 104 dynes/cm2, or a loss tangent no greater than 1 at 23xc2x0 C. and a frequency of 1 Hz. The amount of the at least one thermoplastic material is preferably from about 1 to 50 parts per hundred of the total parts of the rubber.
In one embodiment, the at least one rubber is selected from the group consisting of polybutadiene, polyisoprene, ethylene-propylene, styrene-butadiene, ethylene-propylene-diene rubber, a polymer of ethylene-propylene diene monomer, styrene-ethylene -butylene-styrene copolymer, and mixtures thereof, including functionalized derivatives thereof.
In another embodiment, the core has a diameter of about 1.55 inches or less.
The outer cover preferably includes a castable reactive liquid material. In one embodiment, the castable reactive liquid material is cast polyurethane. The outer cover preferably has a hardness from about 30 Shore D to about 60 Shore D. In one embodiment, the outer cover has a thickness from about 0.02 inches to about 0.045 inches.
In one embodiment, the inner cover includes at least one material selected from the group consisting of ionomers, thermoplastic or thermoset polyurethanes, polyetheresters, polyetheramides, or polyesters, dynamically vulcanized elastomers, functionalized styrene-butadiene elastomers, metallocene polymers, polyamides such as nylons, acrylonitrile butadiene-styrene copolymers (ABS), and blends thereof. In another embodiment, the inner cover has at least one of a hardness of about 65 Shore D or greater. In yet another embodiment, the inner cover has a thickness from about 0.01 inches to about 0.05 inches.
The present invention is further directed to a method of forming a golf ball including the steps of: forming a first mixture including at least one rubber and at least one thermoplastic material; mixing said first mixture at a first temperature sufficient to allow substantially homogeneous mixing of said first mixture; cooling said first mixture to a second temperature, wherein said second temperature is below an activation temperature of a free-radical initiator capable of facilitating crosslinking of the first mixture; forming a second mixture by adding the first mixture to the free-radical initiator having the activation temperature at a temperature above the second temperature; and shaping and heating the second mixture to at least the activation temperature to crosslink the second mixture so as to form a portion of a golf ball core; forming an inner cover disposed about the golf ball core; and forming an outer cover thereon. The at least one thermoplastic material preferably includes a thermoplastic elastomer.